Grinding disc for grinding mills



Aug. 30, 1960 Filed July 9, 1956 2 Sheets-Sheet 1 Aug. 30 1960 TOMIZO SAITO 7 2,950,872

GRINDING DISC FOR GRINDING MILLS Filed July 9, 1956 2 Sheets-Sheet 2 United States Patnt O GRINDING DISC FOR GRINDING MHLLS Tomizo Saito, 46 4-chome, Higashi-Shinagawa, Tokyo, Japan Filed July 9, 1956, Ser. No. 596,760

2 Claims. (Cl. 241-296) The present invention relates to a grinding disc for grinding mills, and more particularly to grinding mills wherein raw materials are ground by rubbing them between two oppositely arranged toothed discs, one of which is rotary and the other stationary.

Heretofore, rotary grinding discs have been used in grinding mills as specified above, wherein radial grooves are provided extending from the center to the external periphery of said disc grinding mills. However, as in such discs wood chip or pulp is ground by rubbing it in only one direction, the chip or pulp has a tendency to clog the radial grooves, while being ground, which not only decreases the grinding efiiciency remarkably, but also wastes the power necessary for the rotation of the grinding discs and makes it diflicult to get a desired ground material. Alternatively, there are types of discs for impact rotary grinding disc mills, which are provided with numbers of projections extending from the center towards the external periphery of said discs. in these latter grinding discs, substance to be ground is ground due to the impact of every projecting member. When wood chips, knots or pulps are ground thereby, fibers are cut. Therefore, this type of grinding disc mill is not suitable for grinding wood chips, knots or pulps. In addition, these impact rotary grinding disc mills have their disadvantages of high consumption of power, because the rotary grinding disc crushes material by means of impact.

All such disadvantages are eliminated according to the present invention wherein a circular grinding disc for a grinding mill has parallel groups of grinding projections elliptically disposed on an annular grinding pontion on one of its faces. At least some of such individual projections extend substantially radially of the grinding disc. With two of such discs, 2. fixed and a rotary disc, coactively and conventionally mounted with respect to each other, each quarter rotation of the rotary disc produces a radial component tending to slide the material along the spaces between the projections. This is so because of the elliptical positioning of the grinding projections and the circular movement of the rotary disc. Thus, the material is prevented from wedging in between the projections, the grinding efiiciency of which is maintained.

The present invention is explained in further detail with respect to the accompanying drawings illustrating one embodiment of this invention, of which Fig. l is a plan view of a grinding mill fitted with a grinding disc of this invention;

Fig. 2 is an elevation showing a part thereof in section;

Fig. 3 is an elevation of the grinding disc of this invention;

Fig. 4 is cross section of the toothed portions of the rotary and stationary discs;

Fig. 5 is an enlarged elevation view of part of the grinding disc of this invention showing the grinding projections.

Referring to Fig. 1, raw material to be ground, such as wood knots, chips or pulps and the like, is fed in a grinding drum 6 through an appropriate hopper arranged at Patented Aug. 30, 1960 the top of said grinding drum 6. A rotary screw conveyer 7 is revolved through a transmission gear mechanism (not shown) and raw material is continuously fed from the outlet 9 of aforesaid rotary screw conveyer into the inlet of a rotary grinder 8. The material in rotary grinder 8 is introduced in a clearance C between rotary grinding disc 1 and stationary grinding disc 5 and ground by revolving the rotary grinding disc I mounted on a revolving shaft 11 and discharged from an outlet 13.

The rotary grinding disc 1 is, as shown in Pig. 3, provided at the periphery thereof with an annular grinding portion 2 on one face thereof. Substantially radially extending grinding projections 4 are formed on the grinding portion 2 of the grinding disc 1, in a plurality of elliptical rings symmetrically surrounding the center of the disc, as is clearly shown in Fig. 3. Adjacent rings of grinding projections are separated by oppositely beveled ends of the grinding projections (as best seen in Fig. 5) terminating in elliptical lines 3 on the surface of the grinding portion 2 from which the projections extend. As will be apparent from Fig. 5, the grinding projections of the outer elliptical rings are finer and more numerous than those of the inner elliptical rings.

The stationary grinding disc 5 is similarly formed, and its relation to the disc 1 is illustrated in Figs. 2 and 4.

Now, the function of the grinding disc mill according to the present invention will be described as follows: When the rotary grinding disc 1, which is arranged in opposition to the stationary disc 5 with a clearance C therebetween, as shown in Fig. 4, is revolved the complementary groups of projections on the respective discs, in addition to the normal relative angular displacement due to the relative rotation of the discs, will also be displaced radially relative to each other due to the ovality of the groups of projections on the respective discs, and will, in fact, only match-up or be directly opposite each other twice in every rotation of the rotary disc. Thus when raw material for grinding such as wood knots, chips or pulp is fed between the discs this relative radial displacement of the complementary groups of projections tends to prevent clogging of the projections that would otherwise occur if the complementary projections were continuously in direct opposition to each other during the whole grinding operation.

Therefore, according to the present invention, grinding can be carried out in a short period of time Without the quality of the material being ground deteriorating and without lowering the grinding efiiciency due to the ground mass remaining clogged between the projections on the opposing discs. At the same time, the power required for driving the discs remains low and economical.

What I claim is:

1. A grinding disc for rotary disc grinding mills, said disc having an annular grinding portion on one face thereof provided with substantially radially extending grinding projections formed in a plurality of elliptical rings symmetrically surrounding the center of the disc, such rings being separated by oppositely beveled ends of the projections in adjacent elliptical rings.

2. A grinding disc according to claim 1, wherein the grinding projections of the outer elliptical rings are finer and more numerous than those of the inner elliptical rings.

References Cited in the file of this patent 

